Well, clearly Light and Sayu are the main characters. They are the focus of the fanfiction and the story usually revolves around their relationship, actions, and interactions.
Perhaps there's a story where Sayu discovers a hidden side of Light that no one else knows. This leads to a series of events that change their relationship dynamic in unexpected ways. For example, Light might be secretly working on a project to save their town from a disaster and Sayu gets involved, strengthening their bond as they strive towards a common goal.
Kaname is typically seen as a mysterious and powerful figure. His allure is often a central part of his character in fanfictions. Yuki, on the other hand, has a certain naivete combined with a growing sense of self - discovery. In kaname and yuki lemon fanfiction, unfortunately, these traits can sometimes be distorted to fit into inappropriate scenarios. In proper fanfictions, we can see how Kaname's loyalty to Yuki and Yuki's ability to bring out the best in Kaname are important aspects of their relationship.
Yes, there are some interesting ones. You can start by looking on fanfiction.net. There are a variety of stories that explore the relationship between Sayu and L in different ways, from angsty dramas to more light - hearted takes on their interactions.
The unique aspect is that it combines two very different characters. Sayu is a more innocent and normal girl in the Death Note world, while L is this super intelligent and eccentric detective. Their pairing creates a contrast that can lead to really interesting storylines.
There could be his vampire friends or family members. They might be there to support him during the ritual or perhaps they are part of the ritual itself.
There very well could be. Fanfiction allows for all kinds of imaginative pairings and scenarios. Given the popularity of both Harry Potter and the character Kaname Tosen, it's possible that a fan has taken the liberty to write a story that combines the two in some way. It could involve Harry Potter in a world influenced by Kaname Tosen's characteristics or a more direct interaction between the two.
A great fanfiction plot could be that Kaname and Zero get transported to a parallel dimension. In this new world, their usual vampire - hunter roles don't exist. They are just two individuals who meet by chance. As they explore this strange new place together, they start to fall in love.
The OC could be characterized as extremely headstrong. For example, she doesn't fear Kaname's vampire status and often challenges his decisions. This would make Kaname, who is used to being in control, both frustrated and intrigued. It would add an interesting dynamic to their relationship as he tries to figure her out.
Their relationship would become extremely complex. If Zero were pregnant, they would have to rely on each other more. Kaname, who might have been somewhat aloof before, would likely become more protective. Zero, on the other hand, would have to deal with his own feelings of vulnerability and dependence, which could be a big change from his usually tough - guy image.